Fig 1.
Permanent dentition of a Baltic grey seal (Halichoerus grypus grypus; specimen ZMUC CN 1157, juvenile male).
(a) Maxillary dentition. (b) Mandibular dentition.
Fig 2.
Map indicating the localities (asterisks) where the Baltic grey seals (Halichoerus grypus grypus) had been collected in 1889–1890.
Five skulls belonged to animals culled on Rødsand sandbank (locality 1), one to an animal culled near Faxe on Sjaelland (locality 2), and one to an animal from Christiansø on Bornholm (locality 3).
Table 1.
List of Baltic grey seals (Halichoerus grypus grypus) skulls from the collection of the Natural History Museum of Denmark, University of Copenhagen (ZMUC) analyzed in the present study.
All teeth present in the specimens belonged to the permanent dentition, and no persistent deciduous teeth were recorded. The labeling is given as it appears on the skulls and the tags (Nobr = November, Dcbr = December).
Fig 3.
Exposure of the pulp cavities through openings at the crown tips in permanent maxillary teeth of juvenile Baltic grey seals (Halichoerus grypus grypus) from the 19th century.
(a) Ventral view of the incisive and anterior maxillary region of specimen ZMUC 424. Note openings at the crown tips of all six maxillary I and both maxillary C. (b) Ventral view of the incisive and anterior maxillary region of specimen ZMUC 693. Note openings at the crown tips of all six I (very small in both I1) and both maxillary C. (c) Ventral view of the incisive and anterior maxillary region of specimen ZMUC 139. Note openings at the crown tips of both I3 and maxillary C, the right P1 and P2, and the left P2 and increased wear of these teeth. Both I1, both I2, the left P1 and the right P3 are missing due to postmortem loss, as is evidenced by the unfilled and sharp-edged alveoli of these teeth. (d) Radiograph (lateromedial projection) of the bones of the anterior facial region of specimen ZMUC 139. Note thin walls and wide apical foramen of the right maxillary C as well as marked radiolucency around its root apex (asterisk) indicative of osteolysis in the course of a periapical inflammation.
Fig 4.
Radiographs (dorsoventral projections) of the anterior portions of the mandibles of four juvenile Baltic grey seals (Halichoerus grypus grypus).
Note thin walls of the mandibular C exhibiting exposed pulp cavities through openings at the crown tips in the two specimens shown in (a) [ZMUC 424] and (b) [ZMUC 303] compared to thicker canine walls in the unaffected “control” specimens shown in (c) [ZMUC 713] and (d) [ZMUC CN 1157]. Arrows: radiolucent areas around the roots of the canines, indicative of pronounced periapical osteolysis. Arrowheads: radiolucency around the root apices of incisors.
Fig 5.
Dorsal view (a) and radiograph (b) of the anterior mandibular region of a juvenile Baltic grey seal (Halichoerus grypus grypus) from the 19th century (specimen ZMUC 155). Note opening into the pulp cavity at the crown tip of the right mandibular C (small arrow in (a)) and radiolucency indicative of pronounced osteolysis around the root of this tooth (asterisk in (b)). In the right mandible, the P1 is missing, most likely due to intravital loss. In the left mandible, the C, P1 and P2 are missing due to intravital loss and the alveoli of these teeth have been filled with bone (large arrows in (a) and (b)).
Fig 6.
Osteolytic lesions in the skulls of juvenile Baltic grey seals (Halichoerus grypus grypus).
(a) Dorsal view of the anterior cranium of a juvenile grey seal from the 19th century (specimen ZMUC 303) showing numerous openings of draining tracts in the incisive bones. (b) Dorsal view of the anterior cranium of a modern juvenile grey seal (specimen ZMUC CN 1157) free of such lesions. (c) Left lateral view of the anterior cranium of a juvenile grey seal from the 19th century (specimen ZMUC 693) showing openings of draining tracts and eroded surface of the maxilla indicative of extended cortical bone resorption. Arrow: root tip of left maxillary C.
Fig 7.
Dorsal (a) and ventral (b) views of the anterior portion of the mandibles of a juvenile Baltic grey seal (Halichoerus grypus grypus) from the 19th century (specimen ZMUC 303) showing signs of suppurative osteomyelitis. (a) Note opening of a draining tract in the left mandible (arrow), and presence of a large (entirely detached) sequestrum (S) and an involucrum (I) in the right mandible. Arrowheads: openings into the pulp cavities at the tips of both mandibular C. The right P1 is missing, most likely due to intravital loss. (b) Note presence of a large sequestrum (asterisk), demarcated by a dividing line but still in place, in the left mandible, and occurrence of an involucrum (I) in the right mandible. An incomplete pathological fracture of the left mandible had occurred along the demarcation line.
Fig 8.
Signs of periapical abscesses and suppurative osteomyelitis in the mandibles of a juvenile Baltic grey seal (Halichoerus grypus grypus) from the 19th century (specimen ZMUC 424).
(a) Dorsal view of anterior mandibular region. Note openings into the pulp cavities at the crown tips of both I1 and both mandibular C, openings of draining tracts (arrowheads), large resorption cavity around the root of the right canine and presence of a large sequestrum in each mandible (asterisks). The loose right P2 was removed to show the resorption cavity. (b) Completely detached sequestrum that was removed from the right mandible. The surface of the sequestrum shows traces of intense resorption.
Fig 9.
Lateral views of the anterior regions of the left mandibles of two juvenile Baltic grey seals (Halichoerus grypus grypus) from the 19th century.
(a) Specimen ZMUC 139; I1, I2, C and P1 are missing, most likely due to intravital loss. Note widened alveolus of the mandibular C and enlargement of the mandible due to apposition of periosteal new bone with numerous small vascular foramina. Porous bone has also been deposited on the wall of the enlarged alveolus. Some of the mental foramina appear enlarged. The changes are indicative of a severe inflammatory process in the anterior mandible. (b) Specimen ZMUC 719, showing the normal condition of the mandible for comparison.
Fig 10.
Permanent maxillary canines of juvenile Baltic grey seals (Halichoerus grypus grypus).
(a) Left maxillary C of specimen ZMUC CN 1157 (top) and right maxillary C of specimen ZMUC 693 (bottom). Root development is more advanced in the canine of ZMUC CN 1157. Arrows: crown-root border; arrowhead: opening into the pulp cavity at the crown tip of the right maxillary C of ZMUC 693. Insert: apical foramina of the canines of ZMUC CN 1157 (left) and ZMUC 693 (right). (b) SEM-BSE image of polished cut surface of the longitudinally sectioned left maxillary C of specimen ZMUC 693, showing external root resorption affecting cementum (Ce) and dentin (D). Asterisk: cementum-dentin-junction. (c) SEM-BSE image showing interglobular dentin (areas where the calcospherites have failed to fuse; these areas appear black in the image) in the root of the left maxillary C of specimen ZMUC 693. Ce: cementum; D: dentin; asterisk: cementum-dentin-junction.
Fig 11.
Longitudinally sectioned right maxillary C of specimen ZMUC 693.
Exposure of the pulp cavity through an opening at the crown tip. D: dentin; E: enamel; arrowheads: crown-root border. Resin-embedded tooth; labial side directed to upper-left corner of image.
Fig 12.
SEM-BSE images of polished cut surface showing the dentin overlying the pulp cavity in permanent maxillary canines of juvenile Baltic grey seals (Halichoerus grypus grypus).
(a) Right maxillary C of specimen ZMUC 693. Note occlusion of many dentinal tubules in juxtapulpal dentin by mineral deposits. As evidenced by its higher brightness, the material occluding the dentinal tubules is more highly mineralized than the surrounding intertubular dentin. PC: resin-filled pulp cavity. (b) Left maxillary C of specimen ZMUC CN 1157. No occlusion of dentinal tubules. D: dentin; PC: resin-filled pulp cavity.
Fig 13.
SEM-BSE image of polished cut surface of the bucco-lingually sectioned M1 of specimen ZMUC 693 showing the dentin overlying the pulp cavity.
Three types of dentin can be distinguished. The primary dentin (PD) is characterized by regularly arranged, straight dentinal tubules, whereas the tubules in the secondary dentin (SD) are curved and arranged somewhat more irregularly. The tertiary dentin (TD) that has been deposited in the pulp horn exhibits only very few tubules. PC: resin-filled pulp cavity. The stippled line indicates the approximate border between secondary and tertiary dentin.
Fig 14.
Enamel structure in longitudinally sectioned teeth of specimen ZMUC 693; SEM-SE images of etched polished cut surface.
(a) buccal enamel of the right M1. The enamel is prismatic and shows Hunter-Schreger bands, i.e., alternating zones of more longitudinally and more transversely sectioned prisms. D: dentin; EDJ: enamel-dentin junction, OES: outer enamel surface; R: resin. (b) labial enamel of the right maxillary C showing zones with transversely (arrowheads) and longitudinally (arrows) sectioned prisms. The outer enamel surface is located to the left of the field of view.
Table 2.
Vickers hardness of enamel and coronal dentin in maxillary canines of two juvenile Baltic grey seals, Halichoerus grypus grypus (left maxillary C of specimen ZMUC CN 1157, right maxillary C of specimen ZMUC 693).